Dynamic array generation fails with over 100 elements

[Steve the Pocket]

So I'm making a heapsort program... all my sort code seems to work just fine. Only problem is, the part where I create the array to test it bombs out whenever the number of elements is over 100. The code is like this...

  short max;
  cout << "\nHeapsort Program\n\n";
  cout << "Enter # of elements to generate: ";
  cin >> max;
  short* unsortedList = new short[max];
 
  cout << "Generating list of integers...";
  for (short x=0; x<max; x++)
  {
    unsortedList[x] = (rand()%100)+1;
  }
  cout << " done.\n\nInitializing sort...";
  //actual sort code follows, of course

...and when I enter a number over 100 for the number of elements, I get this error...

terminate called after throwing an instance of 'std::exception'
what(): St9exception
Initializing sort...Aborted

Bear in mind that printing "Initializing sort..." is actually part of my code. So it throws an exception buts somehow executes the next line anyway. Also, when the number is really high (500,000 for example), it generates this error instead:

terminate called after throwing an instance of 'std::bad_alloc'
what(): St9bad_alloc
Aborted

Note the lack of "Initializing sort..." in this case, meaning it terminated before the next line this time. At first I thought it was just running out of memory, so I changed the ints to shorts (as seen in the code), but it didn't change anything.

Oh, and as a technical point, I'm using Linux GPP, and the use of a pointer is necessary to how the heap works (it's essentially a priority queue).

[weaknessforcats]

I am not getting an error for the number of elements greater than 100. Of couse, the short can only hold a value of 64K which is why the 500000 doesn't work.

I used Visual Studio.NET 2005.

[arnaudk]

I compiled and ran

#include <iostream>
using namespace std;
int main(int argc, char *argv[]) {
    short maX;
    cout << "Enter # of elements to generate: ";
    cin >> maX;
    short* unsortedList = new short[maX];
    cout << "Generating list of integers...";
    for (short x=0; x<maX; x++) unsortedList[x] = (rand()%100)+1;
    cout << " done.\n\nInitializing sort...\n";
    unsigned long int n(0);
    cin.clear();
    for (short x=0; x<maX; x++) {
            n++;
            cout << unsortedList[x] << "\t";
        }
    cout << "\nn = " << n << ". Press enter to continue.\n";
    cin.ignore(100, '\n');
    cin.get();
    return 0;
}
 

without any errors so the errors you apparently have to do with the rest of your program. It therefore makes sense that you see the message "Initializing sort...". Output (ignore line numbers):

Enter # of elements to generate: 20
Generating list of integers... done.
Initializing sort...
42      68      35      1       70      25      79      59      63      65
6       46      82      28      62      92      96      43      28      37
n = 20. Press enter to continue.
 

- The maximum value for a short int is 32767. When you specify a number greater than this, max is implicitly cast into a short int which may in effect be negative. You could then get a memory allocation error which is a fatal error and the program terminates immediately. I suggest you declare maX to be an unsigned long int. On my compiler, I don't get an error but I get an unpredictable number of random integers with the above script (when I entered 500000 I got n = 828 not 500000).
- max() is a method that is part of STL algorithms, perhaps you could use a different variable name.

[Steve the Pocket]

Well, I tried that code in place of mine in the whole program, and then the error occurred when I started the sort instead of before. I don't know why that is, but it got me to checking my Enqueue function. It was then that I realized the problem: I had copied most of the code over from my first heap program, and still had my maxItems=100 line! So I changed maxItems to a parameter on the constructor and it works fine. As usual the problem was something completely unrelated to what I thought it was. Go fig.

It still gives me a "bad_alloc" error when I try to make the array too long (a billion elements bombed out, for example) but I'm pretty sure that's an out-of-memory error. This machine only has, I think, a gig of RAM, and a billion shorts is two gigs right there.

Problem solved. Thanks!